Reversibly caged glutamate: a photochromic agonist of ionotropic glutamate receptors.
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Action Potentials↗
Biomedical subjects
Dirk Trauner
Publications and source records attributed to Dirk Trauner.
Total synthesis of (-)-heptemerone B and (-)-guanacastepene E.
A concise, stereoselective, and convergent total synthesis of the unnatural enantiomer of the neodolastane diterpenoid heptemerone B has been completed. Saponification of (-)-heptemerone afforded (-)-guanacastepene E. The absolute stereochemistry of (-)-heptemerone B was thus established as 5-(S), the same as (-)-guanacastepene E. The longest linear sequence of the synthesis comprises 17 (18) steps from simple known starting materials. Our general synthetic approach integrates a diverse set of reactions, including an intramolecular Heck reaction to create one quaternary stereocenter and a cuprate conjugate addition for the establishment of the other. The central seven-membered ring was closed with an uncommon electrochemical oxidation, whereas the five-membered ring was formed through ring-closing metathesis. The absolute configuration of the two key building blocks was established through an asymmetric reduction and an asymmetric ene reaction.
Cyclization↗
Exploring biosynthetic relationships among furanocembranoids: synthesis of (-)-bipinnatin J, (+)-intricarene, (+)-rubifolide, and (+)-isoepilophodione B.
The asymmetric total synthesis of (-)-bipinnatin J and its conversion into (+)-intricarene through a transannular 1,3-dipolar cycloaddition is described. In addition, the conversion of (-)-bipinnatin J into (+)-rubifolide and (+)-isoepilophodione B is reported. Biosynthetic relationships among furanocembranoids and the possible role of 1,3-dipolar cycloadditions in biosynthesis are discussed. [reaction: see text]
Cyclization↗
Engineering light-gated ion channels.
Ion channels are gated by a variety of stimuli, including ligands, voltage, membrane tension, temperature, and even light. Natural gates can be altered and augmented using synthetic chemistry and molecular biology to develop channels with completely new functional properties. Light-sensitive channels are particularly attractive because optical manipulation offers a high degree of spatial and temporal control. Over the last few decades, several channels have been successfully rendered responsive to light, including the nicotinic acetylcholine receptor, gramicidin A, a voltage-gated potassium channel, an ionotropic glutamate receptor, alpha-hemolysin, and a mechanosensitive channel. Very recently, naturally occurring light-gated cation channels have been discovered. This review covers the molecular principles that guide the engineering of light-gated ion channels for applications in biology and medicine.
Animals↗
Photochemical origin of the immunosuppressive SNF4435C/D and formation of orinocin through "polyene splicing".
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Immunosuppressive Agents↗
Development of a Friedel-Crafts triflation.
The development of a new variant of the Friedel-Crafts reaction that yields 3-aryl enol triflates is described. The reaction is practical, is atom-economical, and works well with electron-rich arene substrates. [reaction: see text].
Alkylation↗
Synthesis of taiwaniaquinoids via Nazarov triflation.
A unified approach toward the taiwaniaquinoids that has yielded four natural products is described. A new variant of the Nazarov reaction with concomitant formation of an enol triflate serves as one of the key steps, considerably shortening the synthetic scheme and providing a general entry into this class of bioactive natural products.
Diterpenes↗
Light-induced depolarization of neurons using a modified Shaker K(+) channel and a molecular photoswitch.
To trigger action potentials in neurons, most investigators use electrical or chemical stimulation. Here we describe an optical stimulation method based on semi-synthetic light-activated ion channels. These SPARK (synthetic photoisomerizable azobenzene-regulated K(+)) channels consist of a synthetic azobenzene-containing photoswitch and a genetically modified Shaker K(+) channel protein. SPARK channels with a wild-type selectivity filter elicit hyperpolarization and suppress action potential firing when activated by 390 nm light. A mutation in the pore converts the K(+)-selective Shaker channel into a nonselective cation channel. Activation of this modified channel with the same wavelength of light elicits depolarization of the membrane potential. Expression of these depolarizing SPARK channels in neurons allows light to rapidly and reversibly trigger action potential firing. Hence, hyper- and depolarizing SPARK channels provide a means for eliciting opposite effects on neurons in response to the same light stimulus.
Action Potentials↗
Expedient synthesis of (+/-)-bipinnatin J.
[reaction: see text] A nine-step, stereoselective synthesis of bipinnatin J is described, which features a ruthenium-catalyzed Alder-ene reaction, a Stille cross coupling, and an intramolecular Nozaki-Hiyama-Kishi allylation as key steps. The biosynthetic relationship between bipinnatin J and complex polycyclic diterpenes isolated from gorgonian corals is discussed.
Animals↗
Synthetic studies toward the haouamines.
[reaction: see text] A concise synthetic approach toward the haouamines based on Stork-Danheiser alkylation and Friedel-Crafts chemistry is described. A novel electrophilic aromatic substitution with concomitant formation of an enol triflate is reported.
Journal Article↗
Pericyclic reactions of prenylated naphthoquinones: biomimetic syntheses of mollugin and microphyllaquinone.
[reaction: see text] A total synthesis of the bioactive naphthohydroquinone mollugin and the related naphthoquinone dimer microphyllaquinone is described. Both syntheses exploit the propensity of prenylated quinones to undergo tautomerization/oxa 6pi-electrocyclizations.
Cyclization↗
Allosteric control of an ionotropic glutamate receptor with an optical switch.
The precise regulation of protein activity is fundamental to life. The allosteric control of an active site by a remote regulatory binding site is a mechanism of regulation found across protein classes, from enzymes to motors to signaling proteins. We describe a general approach for manipulating allosteric control using synthetic optical switches. Our strategy is exemplified by a ligand-gated ion channel of central importance in neuroscience, the ionotropic glutamate receptor (iGluR). Using structure-based design, we have modified its ubiquitous clamshell-type ligand-binding domain to develop a light-activated channel, which we call LiGluR. An agonist is covalently tethered to the protein through an azobenzene moiety, which functions as the optical switch. The agonist is reversibly presented to the binding site upon photoisomerization, initiating clamshell domain closure and concomitant channel gating. Photoswitching occurs on a millisecond timescale, with channel conductances that reflect the photostationary state of the azobenzene at a given wavelength. Our device has potential uses not only in biology but also in bioelectronics and nanotechnology.
Allosteric Regulation↗
Concise synthesis of (+/-)-rhazinilam through direct coupling.
[reaction: see text] A concise synthesis of rhazinilam through direct, palladium-catalyzed, intramolecular coupling is described.
Alkaloids↗
Photosensitized conversion of 9,10-deoxytridachione to photodeoxytridachione.
[reaction: see text] The photochemical conversion of 9,10-deoxytridachione to photodeoxytridachione has been photosensitized. The conversion was also quenched by piperylene. Photodeoxytridachione was produced in good yields under conditions in which only the cyclohexadiene group is sensitized. The results show that some, and perhaps all, of the photoreactions of 9,10-deoxytridachione occur through a triplet excited state. The mechanistic and biosynthetic implications of these results are discussed.
Alkadienes↗
Total synthesis of (-)-SNF4435 C and (+)-SNF4435 D.
[reaction: see text] A convergent, biomimetic total synthesis of the immunosuppressant polyketides SNF4435 C and D is described. The synthetic pathway features a stereo- and regioselective [3,3]-sigmatropic rearrangement as well as a high-yielding Stille coupling/8pi-6pi electrocyclization cascade.
Crystallography, X-Ray↗
Infrared hole burning and conformational change in a borane-ammonia complex.
The N-D stretching region in the infrared spectrum of the ammonia complex of tris-(2-methoxymethyl-phenol)-borane containing one D atom has been examined. The N-D bands have been hole burned, and the resulting spectra reveal the reorientation kinetics of the ammonia. The ammonia is hydrogen bonded with the bond distances and reorientation barrier typical of other compounds. The N-D stretching frequencies are higher than those of comparison compounds.
Ammonia↗
An electrochemical approach to the guanacastepenes.
An asymmetric approach toward the [6-7-5] ring system of the guanacastepenes is described. [structure: see text]
Catalysis↗
Mining the tetraene manifold: total synthesis of complex pyrones from Placobranchus ocellatus.
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Animals↗